We discuss the link between weight and breast cancer.

Wednesday 26 November 2014      Research blog
Obesity linked to nearly half a million new cases of cancer a year

You may have seen in the papers today that a new study in the Lancet has published estimates on the global burden of cancer attributable to high BMI, or body mass index.  This is a measure of obesity which, as we have mentioned before, is not only a risk factor for breast cancer but many other cancer types. 

Results just in

The top line results are that, worldwide, 481,000 cancer cases each year in adults were found to be attributable to obesity. In the UK, around 8.2% of all cases in women (about 13,000 cases a year) were linked to obesity, compared to the global average of 5.4%.

It’s probably worth explaining how they calculated these estimates. The researchers used the estimated number of people with high BMI (or obesity) from each country taken in 2002 and compared this to the number of new cancer cases appearing in 2012. This allows for a lag time of 10 years between measuring obesity and cancer occurrence.  Importantly, they only looked at cancer types with significant evidence for obesity as a risk factor.

So what did the figures say about breast cancer?

It turns out that postmenopausal breast cancer in women is responsible for the largest number of cancer cases linked to obesity in the world. When the researchers factored in the average population obesity levels from 1982, what they found was particularly interesting. If obesity had stayed at 1982 levels, rather than rising to the recorded levels in 2002, then a quarter of all obesity-related cancers could have been prevented. For breast cancer this amounts to about 28,000 new cases worldwide.

These statistics are alarming. In the UK, we are way above the world average for obesity-linked cancer and what’s more, many of these cases could have been prevented. There needs to be widespread change across all sectors (education, food and drink industry, government etc.) or it is highly likely that in 10 years’ time these statistics will be even worse. Probably most important of all is that the individuals get the support and help they need to take control of their own health.

What do we know about weight and breast cancer?

The evidence shows that by maintaining a healthy weight throughout your life, you can reduce your risk of developing breast cancer after the menopause. Obesity after menopause significantly increases a woman’s risk of breast cancer. We would expect that in a group of 100 women over 50 years old who have a normal BMI, around eight or nine would develop breast cancer. In a similar-sized group of women with a high BMI we would expect 11 or 12 women to develop breast cancer.

As a breast cancer charity we are committed not only to research, but also to raising awareness of obesity as a risk factor for the disease and providing advice on what lifestyle changes could be made to help maintain a healthy weight. We’ve started a campaign called ‘Raise your pulse, reduce your risk’ which encourages women to take up physical activity to help reduce their risk of breast cancer. Our website ‘BRISK’ has all the info behind the stats and a handy activity tracker to help keep women active. We have also been working with an organisation called Balance North East to help promote moderate alcohol consumption through a campaign called ‘Think Twice’.

What are your thoughts? How can society tackle the rising obesity problem?
Have your say in the comments below.

Dr Matthew Lam is Breakthrough Breast Cancer's Senior Research Officer